This invention relates generally to liquid filtration systems and, more specifically, to traveling bridge-type cleaning devices for sequentially cleaning a plurality of downward flow, suspended solids filter units.
It is well known in the art to utilize filtration tanks divided into a plurality of filter cells, one adjacent the other, and all containing a multi-layer or single layer arrangement of granular filter media such as sand, gravel and the like. In downward flow filtration systems of this type, water or other liquid containing suspended solid particles is introduced into the filtration tank from above and clarified water is drawn off from a chamber beneath the filter cells. During downward flow through the individual cells, particulate matter is entrapped within the layers of granular filter media. Eventually, the particulate matter clogs the filter media, thereby reducing the filtering capability of the system. Thus, there is a need for periodic cleaning of the filter cells. It is also known to maintain such units in continuous operation during cleaning by the use of traveling bridge devices which move from one filter cell to the next, to clean individual cells while permitting the filtration process to continue in the remaining cells.
Examples of traveling bridge apparatus of this type may be seen in U.S. Pat. Nos. 4,540,487; 4,486,307; 4,133,766; 3,984,326; 2,235,227, and 649,409. Typically, traveling bridge systems include an overhead carriage, movable along tracks, guideways or the like, which carries, e.g., a backwash hood successively engageable with the upper end of each filter cell. For a downflow type filter, water or other treatment liquid is generally introduced into the cell from below, in a counterflow arrangement to the normal filtering direction. The backwash hood typically includes a suction head for drawing out fluid and debris forced to the surface of the filter cell as a result of the backwash. As the backwash of individual cells are completed, the traveling bridge will index the backwash hood to the next adjacent cell. See, for example, U.S. Pat. No. 4,308,141, in which a modular filter system is disclosed, and wherein a traveling bridge type backwash system is indexed to successive filter units.
In the present invention, a unique combination of filter cell cleaning devices are provided in a traveling bridge configuration. Specifically, a dual hood assembly is provided wherein an air scour operation precedes a backwash operation during the successive cleaning of each individual cell.
In one exemplary embodiment, an elongated, rectangular filtration tank is divided into a plurality of individual cells by a plurality of laterally spaced, substantially parallel partitions extending across the width of the tank. The tank is further provided with tracks or guideways supporting a traveling bridge for movement along the top of the tank, in a direction transverse to the orientation of the upright partitions. The traveling bridge includes a carriage which carries air scour means as well as backwash means, arranged for sequential engagement with each filter cell.
The air scour means includes an air scour hood having a pair of vertical walls longitudinally spaced apart a distance corresponding to the width of the individual filter cell partitions. The air scour hood is provided with sealing means, such as rubber gaskets, at the lower end of each of the vertical walls, which engage the upper surfaces of the cell partition walls, thereby isolating the cell from the remaining cells. The air scour hood is open to atmosphere at its upper end, and is connected to an air scour supply conduit extending between the hood and the carriage. The air scour supply conduit is connected at its upper end to a pump or other source of pressurized air mounted on the carriage. The lower end of the air scour outlet conduit is provided with a flanged head or boot adapted to successively engage vertical risers extending upwardly from the lower end of each cell to the upper end thereof, approximately mid-way along the length of the cell. In this first exemplary embodiment, a horizontal air supply conduit is connected to the lower end of each vertical riser and extends across the lower half of each filter cell, preferably in the lower portion of an intermediate layer of filter media, and in a direction substantially parallel to the cell partitions. Each such horizontal conduit is provided with a plurality of perforations along its length and about its periphery so that, when air is supplied to the filter cell it will be uniformly discharged along the cell, preferably within the intermediate layer of filter media. As the air flows upwardly through the filter media, it dislodges particulate matter which will be ultimately backwashed in the next successive step. The air utilized in the air scour step is eventually vented to atmosphere through the open top of the air scour hood.
Also mounted on the traveling bridge carriage is a conventional backwashing device including a backwash hood and a horizontal backwash suction conduit. The backwash hood comprises conical, upwardly inclined side walls which terminate, at their lower ends, with sealing means such as rubber gaskets which engage the cell partitions to isolate the respective cells from the remaining cells. Preferably, one of the conical side walls merges with one of the air scour hood walls so that one of the sealing means is common to both hoods. In other words, the dual hood assembly need only employ three sealing devices to isolate two adjacent filter cells.
The horizontal backwash suction conduit is located within the hood section per se, and is connected substantially midway along its length to a vertical suction conduit extending upwardly, through the hood, to the carriage. The carriage also mounts a suction pump, the outlet side being connected to the vertical suction conduit. Like the horizontal air supply conduits, the horizontal backwash conduit has a length substantially equal to the length of the individual cells. The suction conduit is also provided with a plurality of uniformly arranged apertures extending along its length and about its periphery to uniformly draw liquid and accompanying debris out of the filter cell in a direction opposite the normal filter flow direction to thoroughly backwash the filter media.
The combination of an air scour/backwash operation, carried out successively for each filter cell, quickly and effectively cleans each filter cell without disturbing the overall operation of the liquid filtration system.
It will be appreciated that in order to index the dual hood assembly to successive cells along the filtration tank, the assembly is reciprocable vertically by a distance sufficient to enable the dual hood structures to disengage from the cell partitions or walls, and to clear the adjacent cell partitions during lateral movement to the next cell. To this end, a portions of the vertical air scour conduit and vertical backwash conduit, respectively, may be provided with flexible, e.g., bellows-type connectors which permit a relatively small degree of vertical movement of the dual hood structures vis-a-vis the vertically fixed carriage.
In a related aspect of the invention, the vertical air scour riser provided in each filter cell is fitted with a spring loaded valve at its upper end, the valve opening in response to air pressure supplied through the air scour supply conduit when the riser and supply conduit are in engagement. It is also a feature of this invention that the air scour supply conduit boot mount a squeegee-type device to remove debris from the upper surface of the valve. In an alternative mode, the squeegee-type device may be eliminated and the air scour pump can be actuated just prior to engagement of the air supply conduit and the riser valve to supply a burst of air which will clean the valve head.
In an alternative embodiment of the invention, the air scour pump is located on the ground, and each individual cell unit is provided with a horizontal air scour conduit which extends along the length of each cell and out of the side wall of the tank where each of the air scour inlet conduits is joined to a common manifold extending from an air supply source. A manually operable valve is provided in each of the inlet conduits adjacent the side of the tank and aligned along a longitudinally directed guide rail. At the same time, the traveling bridge is provided with a valve actuator which includes an automatically rotatable device which is designed to engage the manually operable valve and, in accordance with an automatic programmable control sequence, open the valve to initiate the air scour operation, and thereafter close the valve when the operation is completed. In this second embodiment, the overhead carriage continues to mount the backwash hood and backwash pump, as well as the air scour hood.
Accordingly, in its broadest aspect, the present invention relates to a traveling bridge filter cleaning system including a liquid filtration tank divided into a plurality of adjacent filter cells, each of the cells containing filter media, a traveling bridge carriage located above the tank and movable along the tank, the carriage mounting air scour means comprising an air scour hood adapted to sealingly engage each of said cells, and backwash means comprising a backwash hood also adapted to sealingly engage an adjacent one of the cells.
It will therefore be appreciated that the present invention provides a unique combination of air scour and backwash means in a traveling bridge filter cleaning system which effectively cleans successive cells of a multi-cell tank without disturbing the filtering process in the remaining cells.
Additional objects and advantages of the subject invention will become apparent from the detailed description which follows.